The present invention relates to a fixed torque spring clutch which is inexpensive, in capable of transmitting very constant torque and has a long life.
The inventor has developed a fixed spring clutch (see FIG. 10) and filed in The U.S. Patent And Trademark Office as follows:
______________________________________ Application number: 07/516,595 Application date: April 30, 1990 Title: A FIXED TORQUE SPRING CLUTCH AND A WINDER HAVING THE SAME Inventor: Fumito KOMATSU ______________________________________
The spring clutch shown in FIG. 10 has a coil spring 14. The coil spring 14 consists of a first clamping section A and a second clamping section B. The first clamping section A of the coil spring 14 is wound around a shaft section 12 of a second rotor 11. There is formed an engage piece 16 at the end of the second clamping section B. The engage piece 16 contacts a limit piece 18 provided in a flange section 17 of a first rotor 10. There is provided a release piece 19 in the first rotor 10. The release piece 19 deviates away from the limit piece 18 at an angle .alpha.. The release piece 19 rotates in the direction of loosening the first clamping section A so as to contact an engage section, which is formed at the end of the first clamping section A.
By rotating either the first rotor 10 or the second rotor 11 in the prescribed direction with respect to the other, the first clamping section A of the coil spring 14 winds around the shaft section 12. The end of the second clamping section B is caught by the limit piece 18, so that the torque of the second clamping section B rises in accordance with the spring characteristics. When the release piece 19 contacts the first clamping section A, the first clamping section A is loosened. In spite of loosening the clamping section A, the torque of the second clamping section B continues to rise while the clamping force of the first clamping section A remains greater than the torque of the second clamping section B. When the clamping force of the first clamping section A and the torque of the second clamping section B are balanced, the first clamping section A then slips on the shaft section 12, so that the torque is stabilized.
The total torque is primarily affected by the torque of the second clamping section B; the torque of the first clamping section A is relatively small. Variations in torque among the clutches of the present invention are minimized, therefore, in spite of any differences in diameter of the first clamping sections.
Note that if the second clamping section B of the coil spring 14, which is previously wound to have a torsion slightly less than the prescribed operating torque, is attached between the limit piece 18 and a stopper 20 (see FIG. 11), the torque quickly reaches the prescribed value upon rotation of first rotor 10.
In the fixed torque spring clutch shown in FIGS. 10 and 11, the torque can be freely defined by selecting the spring characteristics of the second clamping section B.
However, the fixed torque spring clutch has following disadvantages:
(1) The friction caused by slippage of the shaft section 12 in the first clamping section A creates heat and the frictional coefficient .mu. consequently changes, so that the torque gradually rises during operation. PA1 (2) The clamping force of the first clamping section A is lost with operation due to abrasion caused by said slippage. PA1 a first rotor; PA1 a second rotor being coaxial to the first rotor; PA1 a shaft section being provided to one of the rotors; PA1 a plurality of catch sections being provided to the other rotor; and PA1 a coil spring being provided over the shaft section, the both ends of the coil spring being retained by the catch sections in clamping status thereof, the coil spring having a first clamping section for clamping the shaft section with prescribed clamping force when the coil spring is provided over the shaft section, and a second clamping section whose inner diameter is larger than the diameter of the corresponding part of the shaft section when the coil spring is provided thereover. PA1 a first rotor; PA1 a second rotor being coaxial to the first rotor; PA1 a hollow cylindrical shaft section being provided to one of the rotors; PA1 a plurality of catch sections being provided to the other rotor; and PA1 a coil spring being provided in the shaft section, the both ends of said coil spring being caught by the catch sections in diameter enlargement status thereof, the coil spring having a first clamping section for elastically contacting the inner face of the shaft section when the coil spring is provided in the shaft section, and a second clamping section whose outer diameter is smaller than the inner diameter of the corresponding part of the shaft section when the coil spring is provided therein.